1. Field of the Invention
This invention relates to a method of preconditioning a resin and removing total organic carbon (TOC) impurities from a hydrogen peroxide solution using the preconditioned resin. The invention has particular applicability in the semiconductor manufacturing industry for the removal of total organic carbon impurities from a hydrogen peroxide solution.
2. Description of the Related Art
Hydrogen peroxide (H2O2) is an important chemical in the semiconductor manufacturing industry. It is commonly used in solutions employed in wafer cleaning processes which are conducted in wet processing stations. For example, the well known piranha cleaning process employs a 30% solution of hydrogen peroxide and sulfuric acid (H2SO4)in a ratio of 3:7. Other processes employing hydrogen peroxide solutions include, for example, the RCA SC-1 cleaning process which involves a solution of ammonium hydroxide (NH4OH) and hydrogen peroxide in a ratio of 5:1:1, and the RCA SC-2 clean, which uses a solution of hydrochloric acid (HCl) and hydrogen peroxide in a ratio of 6:1:1.
To reduce the probability of device failure, it is important in semiconductor device fabrication that the materials which contact the wafers being treated be of very high purity. The extreme purity levels required in semiconductor manufacturing are rare and unique among industrial processes. While existing techniques of purifying hydrogen peroxide may significantly reduce the amount of contaminants, solutions of even greater purity are desirable.
Commercial grade hydrogen peroxide is generally produced by the so-called anthraquinone method. This method involves auto-oxidation of anthraquinone, which results in the presence of large amounts of organic contaminants in solution. The contaminants may either originate from the anthraquinone or from the organic solvents used in preparing the hydrogen peroxide solution from the anthraquinone. Typical organic contaminants in hydrogen peroxide solutions include, for example, alcohols, aldehydes and other organic substances which typically cannot be effectively removed by ion exchange resins.
It is conventional practice to treat hydrogen peroxide prior to shipping to remove organic impurities. For example, it is known to remove organic contaminants by extraction with a water miscible organic solvent. However, the purified solution still contains organic impurities in amounts that are not acceptable for use in the semiconductor industry.
One method for significantly decreasing the amount of organic impurities in a hydrogen peroxide solution involves contacting the solution with a resin which can absorb the organic contaminants and separate them from the solution. Hydrogen peroxide solutions purified in this manner can achieve high purity levels with respect to TOC""s.
There are, however, various problems associated with the use of absorbent resins to remove organic impurities from an aqueous hydrogen peroxide solution. For example, resins used to treat hydrogen peroxide for removal of impurities may contain metals and bases due to manufacturing and/or storage procedures. When the hydrogen peroxide solution is brought into contact with the resin, the solution is prone to decomposition. Such decomposition is further accelerated due to the basic nature of and presence of metals in the resin, which catalyze the hydrogen decomposition.
Decomposition of the hydrogen peroxide solution can be particularly problematic as a result of the exothermic nature of the reaction. The temperature near the zone of contact between the resin and the solution can increase very rapidly, increasing the rate of decomposition. This can result in a self-accelerating reaction, possibly terminating in an explosion of the purification equipment.
Thus, there remains a need for a resin-based method and system for removing organic impurities from a hydrogen peroxide solution in a safe and cost-effective manner.
Copending application Ser. No. 09/824,765 Attorney Docket No. 016499-526, the contents of which are hereby incorporated by reference in their entirety, provides novel methods of preconditioning a resin useful for removal of organic impurities from a hydrogen peroxide solution. The preconditioning method is based on treating a resin with a solution of a strong acid to remove contaminants such as metal impurities from the resin. Hydrogen peroxide decomposition upon contact with the resin during purification can thereby be minimized. This resin preconditioning method provides vast improvements over the methods previously known in the art. However, the method requires rinsing the resin with deionized water after the acid treatment and prior to passing a hydrogen peroxide solution to be purified through the resin.
It is highly desirable to conduct the resin preconditioning in situ in the unit in which the resin is to be utilized. However, the need for a rinsing step after the acid treatment in the above resin preconditioning method introduces downtime in operating the unit due to the extra rinsing step prior to hydrogen peroxide purification.
It is an object of the present invention to overcome or conspicuously ameliorate the problems with the related art. In particular, the invention effectively minimizes downtime in hydrogen peroxide purification and maximizes the efficiency of resin hydrogen peroxide units including in situ resin preconditioning.
Other objects and aspects of the present invention will become apparent to one of ordinary skill in the art on a review of the specification, drawings and claims appended hereto.
The present invention provides a method of purifying a hydrogen peroxide solution. The method comprises preconditioning a resin by a method comprising (i) washing the resin with deionized water to produce a washed resin, and (ii) contacting an effective amount of a preconditioning hydrogen peroxide solution with the washed resin to remove impurities from the washed resin, thereby producing a preconditioned resin.
The method also comprises passing a hydrogen peroxide solution to be purified through a bed of the preconditioned resin to form a hydrogen peroxide solution having a TOC content lower that a TOC content of the hydrogen peroxide solution to be purified, and passing the hydrogen peroxide solution having a TOC content lower than the TOC content of the hydrogen peroxide solution to be purified through one or more ion-exchange resin beds. The preconditioning hydrogen peroxide solution does not pass through the ion exchange resin beds.
In accordance with one aspect of the invention, the hydrogen peroxide solution having a TOC content lower than the TOC content of the hydrogen peroxide solution to be purified is directed to a point of use in a semiconductor manufacturing facility through a conduit disposed between the bed of preconditioned resin and the point of use, with or without passing the hydrogen peroxide solution having a TOC content lower than a TOC content of the hydrogen peroxide solution to be purified through one or more ion-exchange resin beds, wherein the preconditioning hydrogen peroxide solution does not pass through the one or more ion-exchange resin beds and is not directed to the point of use.
In accordance with a further aspect of the invention, the preconditioning hydrogen peroxide solution and the hydrogen peroxide solution to be purified are supplied from the same hydrogen peroxide source.
In accordance with a still further aspect of the invention, the preconditioned resin has a TOC removal capacity of about 50% or more of the resin""s TOC removal capacity prior to preconditioning, and/or a residual impurity level of about 100 ppb or less.
In accordance with a still further aspect of the invention, a valve in a conduit between the resin bed and the ion-exchange resin beds is opened after resin preconditioning is completed.
In accordance with yet a further aspect of the invention, the preconditioning hydrogen peroxide solution is assayed after passage through the resin, and a valve is opened when a predetermined hydrogen peroxide concentration has been reached.